Various stirrers have been proposed for emulsification, dispersion, or mixing of a fluid, and today it is requested that a fluid to be processed which contains a material having a small particle diameter such as a nanoparticle is processed sufficiently well.
For example, a bead mill and a homogenizer are known as examples among many stirrers widely known.
In a bead mill, however, performance deterioration due to destruction and damage of a crystal condition of particle's surface has been a problem. Another significant problem is that a foreign matter is generated. In a high pressure homogenizer, problems relating to stable operation and requirement of a significantly large energy are yet to be solved.
A rotary homogenizer has been used as a pre-mixer in the past; but this requires a finishing machine to accomplish dispersion and emulsification to a nanometer level.
In view of the above situation, inventors of the present invention proposed the stirrer shown in Patent Documents 1 and 2. This stirrer is equipped with a rotor having plural blades and a screen having plural slits which is arranged around the rotor. The rotor and the screen rotate relative to each other, whereby shearing a fluid to be processed in a very narrow space formed between the blades and the inner wall of the screen which has slits so that the fluid to be processed is discharged from inside the screen toward outside thereof through the slits as an intermittent jet flow.
In the stirrer like this, as shown in the columns of Background Art of Patent Document 2, the stirring condition thereof has been changed by adjusting the rotation number of the impeller (namely the rotor).
There, it is described, “For example, to consider the case of emulsification, by rotation of the impeller, a fluid is sheared between the inner wall arranged with a discharged part of the stirring chamber and the impeller's edge whereby emulsifying one fluid into the other fluid.
Meanwhile, the emulsification capacity of one particular equipment changes depending on properties of fluids to be processed as well as on a combination of the plural fluids; and therefore, the optimum condition for emulsification capacity needs to be obtained in advance in accordance with the fluid to be processed whereby conforming the equipment to this condition.
In the past, the adjustment has been made by arbitrary setting the impeller's rotation number to secure the maximum point of the emulsification capacity.
This is based on the fact that the elements to determine the emulsification capacity are given by the following parameters.
That is, the processing capacity has been evaluated by values of a shear strength, an energy amount, and a passing number. This shear strength (S) is the value showing the strength of the shear force between the impeller and the inner wall of the stirring chamber, and this can be given by the following equation.S=Ns·v=Ns·π·d·n 
Next, the energy amount (Pv), which is the stirring energy per unit processing quantity, can be given by the following equation.Pv=(P/V)×T=(Np·ρ·n3·d5/V)×T  [Eq. 1]
Then, the passing number (Pn), which is the passing number showing how many times the fluid goes through between the impeller and the inner wall of the stirring chamber, namely the circulation number, can be given by the following equation.Pn=(Q/V)×T=(Nq·n·d3/V)×T  [Eq. 2]
Here, v is the maximum circumferential velocity of the impeller (m/sec), d is the diameter of the impeller (m), and n is the rotation number of the impeller (rps). Further, P is the required stirring energy (kw), Np is the power number, Nq is the discharged coefficient. Further, Q is the discharged amount (m3/sec), Ns is the shear coefficient, and V is the processing amount (m3).
Further, T is the processing time (sec) and ρ is the specific gravity (kg/m3) inherent to the fluid to be processed.
As it can be seen clearly from the above equations, the stirring condition has been changed by adjusting the rotation number (n) of the impeller.”
In the invention according to Patent Document 2, the proposal was made as to the stirrer in which the clearance between the edge of the impeller and the inner wall of the screen can be selected arbitrarily while not only the rotation number of the impeller is controlled but also the necessary energy for processing by stirring and so forth is kept constant, whereby intending to optimize the capacity improvement in accordance with the fluid to be processed.
Further finer microparticles with more uniform particle diameter distribution are required in the fields using microparticles such as chemistry, electric and electronics, motor vehicles, foods, color materials, and pharmaceutical drugs; however, by conventional stirrers having the performances so far disclosed, it has been difficult to achieve emulsification and dispersion with which fine microparticles having the uniform particle diameter distribution can be obtained.
Accordingly, even today the above mentioned high-pressure homogenizer and bead mill are used mainly in most cases in emulsification and dispersion; and thus, problems of the energy cost and contamination by a foreign matter have not been solved yet, and on top of that, naturally the producing process using these equipment tends to become complex.
In Patent Documents 1 and 2 which were filed by the applicant of the present invention, disclosed are the effect of the shear force due to the rotor and the screen and the effect of the intermittent jet flow discharged from the screen. A standard model of the stirrer manufactured and marketed by the present applicant based on these effects is the experimental type having the rotor diameter of 30 mm as the minimum scale. In this model, as the maximum, number of the blades is four, number of the slits formed in the screen is 24, and the rotation number is 21,500 rpm; however, in the model like this, it has been difficult to obtain 35 or more as the frequency Z (kHz) of the intermittent jet flow. The rotation number might be increased further up if so desired; however this caused such problems that it increased the loads to the motor and to the equipment and that it tended to readily increase the energy cost. The same was true for the case that up-scaling was made by increasing the rotor diameter; in this case, although number of the slits of the screen could be increased, because the rotation number was decreased and for other reasons, naturally the frequency Z (kHz) of the intermittent jet flow was less than 35. Therefore, sufficient information has not been obtained yet as to the emulsification and dispersion with the frequency Z of 35 or more.